Field of the Invention
The invention is related to microelectromechanical systems (MEMS).
Description of the Related Art
In general, microelectromechanical systems (MEMS) are very small mechanical devices. Typical MEMS devices include sensors and actuators, which may be used in various applications, e.g., accelerometers, gyroscopes, and pressure sensors. The mechanical device is typically capable of some form of mechanical motion and is formed at the micro-scale using fabrication techniques similar to those utilized in the microelectronic industry, such as thin film deposition and thin film patterning by photolithography and reactive ion etching (RIE).
Certain MEMS devices include a resonator, which may be used in timing devices. The resonator may have a variety of physical shapes, e.g., beams and plates. Referring to FIG. 1, a conventional MEMS device (e.g., MEMS device 100) includes resonator 105 coupled to substrate 102 via anchor 104. During operation, electrode 110 electrostatically drives resonator 105 and electrode 110 to dynamically deflect, which increases a capacitance of resonator 105 when a voltage differential exists between resonator 105 and electrode 110 by decreasing the gap between resonator 105 and electrode 110. Since electrode 110 and resonator 105 are the same height and in the same plane, resonator 105, when driven, deforms laterally across a distance between electrode 110 and a second electrode 111, remaining in a plane of electrode 110. The plane of electrode 110 is a plane substantially parallel to substrate 102. Electrode 111 detects the resonant frequency of resonator 105 as the capacitance varies between resonator 105 and electrode 111 in response to the deflection driven by electrode 110. MEMS device 100 is commonly referred to as an “in-plane” or “lateral” mode resonator because resonator 105 is driven to resonate in a mode where the resonator 105 moves laterally (in direction 109) and remains in the plane of electrode 110.
For some MEMS applications (e.g., a low-power clock source), a low-power, high-Q (i.e., quality factor) oscillator may be required. However, the low-power, high-Q specifications may be difficult to achieve using the conventional MEMS device of FIG. 1. Accordingly, improved MEMS devices are desired.